A significant heat dome is expected to impact the eastern half of the United States, affecting over 230 million people. Temperatures will soar above 90°F, with millions experiencing triple-digit readings. The Midwest will be hit first, with cities like St. Louis and Detroit facing mid- to upper-90s temperatures. By Wednesday, the heat will shift east, potentially breaking records in Washington, Baltimore, Philadelphia, and New York City. Temperatures are predicted to exceed 100°F for several days in these urban centers. Meteorologists are calling this a "mega heat dome," forecasting record daily highs across the entire Eastern Seaboard. Extreme heat and humidity are anticipated through the Fourth of July weekend. The heat dome is expected to persist in the Washington, D.C. area until mid-July. This heat event is considered a seasonal occurrence due to peak summer in North America, with potential El Niño risks noted.